(a) Field of the Invention
This invention relates to a cutting torch for iron and steel metallurgy.
(b) Description of Prior Art
Cutting torches currently used in the field of iron and steel metallurgy for the oxycutting of high thicknesses under heat, or for cold slitting, are generally made of a single material, copper, with a central jet of oxygen and most of them are provided with two heating crowns which concentrically surround the jet of oxygen.
French Patent No. 86.11.008 proposes a new concept of injectors for feeding oxygen to the central heating crown and suggests to make this cutting torch in two parts, thereby permitting to optimize the speeds of exit of the heating gases, while presenting the user with the advantage of only changing the cutting block if something takes place which causes a deterioration of the visible part of the torch.
As previously indicated, the most currently used technology in the designing of cutting torches for high thicknesses is the double heating crown which is concentrically disposed around a central jet of oxygen with an outer crown, in which the flame is very oxydizing, enabling to heat the top of the slab intended to be oxycut, and a heating crown located between the outer crown and the central cutting jet, with highly carburizing flame, to give a long wreath around the cutting jet, the wreath being carried by the cutting jet and penetrating the groove cutting in assisting and heating the middle and bottom part of the groove.
For the jet of oxygen, the so called Laval tuyere is the most currently used to give a high speed of exit without splitting of the jet.
However, the use of a single cutting jet operating at very high speed, and consequently at very high pressure, is limited since it may contribute to produce insufficient heating in the middle part of the groove, which, particularly when cold oxycutting, produces erosions which are detrimental to the quality of the cut.
This is the reason why French patent 87.04.523 has proposed a torch for oxycutting comprising two oxygen cutting jets, between which there is a central duct for a carburizing heating flame, ensuring a resumption of heating in depth in the rough groove cut, which has been produced by the first jet of oxygen and which is terminated with the second jet of oxygen. Such a torch can be made of two parts or of a piece of one single element.
It should be noted that the improvement in heating at the bottom of the groove associated with two jets of high pressure cutting oxygen has permitted to increase the cutting speed by 20% under cold condition and by 10% under hot condition, over the better known processes operating with a single jet.
The Applicant has set up as a goal to simultaneously solve three problems, namely:
Since the production of a cutting duct, in particular the manufacture of the Laval tuyere, is a determining element to obtain good performances (width of groove and cutting speed), this production is delicate and costly, because of the dimensions of the torches which are actually sold, and the invention aims at simplifying this operation.
On the other hand, the user must presently own two types of torches depending on whether he wishes to privilege the cutting speed (torches with two cutting jets) or the width of the groove (torches with single cutting jet), and the invention aims at combining these two functions into a same and single torch.
Finally, by experience, the life of a cutting torch directly depends, under normal conditions of use, on the life of the cutting duct. With the present designs, in cases where performance decreases are observed, after cleaning the torch, one must change the cutting block in the design with a single jet, or the entire torch in the design with two jets, and the invention aims at limiting the number of pieces to be changed. The object is therefore to realize another torch design, enabling to solve the three problems mentioned above, while preserving and even improving, the performances of the two processes and ensuring that the torch is industrially reliable.